Certain objects such as broccoli spears are typically bound together in bunches before they are shipped to a point of sale. Automatic broccoli bunching machines are known. For example, U.S. Pat. No. 4,041,672 discloses a machine having a conveyor belt which carries a plurality of serially mounted pocket members. Each pocket member has mounted thereto a clamping mechanism comprising opposed relatively moveable clamping elements configured to assume an open vegetable receiving position as the pocket member moves past a worker stationed at the machine, and a cam portion that engages a fixed ramp downstream to cause the clamping elements to close about the inserted vegetables. The clamped bunches then pass a circular saw that cuts the stalk ends of the vegetables to a uniform length. After cutting, the stalks may be manually bound with an elastic band while the clamping portions are still held in their closed position. Broccoli spears are inserted head first to facilitate the placement of the elastic bands over the cut stalks. Thus the saw is on the same side of the conveyor as the workers.
While such an automatic bunching machine overcomes many of the problems inherent in manually bunching produce in the field or at an individual work station in a food processing plant, it does not represent the most economical way of carrying out large scale bunching in a substantially automated fashion. For example, the above referenced bunching machine is designed for carrying out a method wherein an elastic band is manually placed over the cut ends of the clamped stalks to hold the bunches together once the clamping portions are released. However, the elastic bands used in such an automated process are prohibitively expensive, their cost typically amounting to tens of thousands of dollars per year when a large scale operation is envisioned.
Automatic tying machines for tying stationary objects are known. These machines typically incorporate a knotting mechanism including rotating knotter bills. In operation, a string retaining mechanism holds the free end of a roll of string while an intermediate portion of the string passes through the eye of a string-carrying needle positioned above an object to be tied. The needle then swings in an arcuate path to a position below the object to form a loop of string thereabout. The string ends pass downwardly into a slot in a sheet metal guide overlying the knotter bills and then under the knotter bills to the retaining mechanism. The needle typically carries a placer foot rigidly attached thereto so that as the needle reaches its extreme of travel, the placer foot effectively closes the slot to define an aperture which constrains the string against lateral movement and prevents its being pushed out of the slot as the knotter bills turn to tie the knot. After the knotter bills have tied the knot, the sheet metal guide moves in a transverse direction to strip the string from the knotter bills.
The cost of string is relatively negligible compared to that of elastic bands. Thus the idea of using an automated tying machine in connection with an automatic bunching machine is attractive, since in addition to reducing labor costs, a tying machine can result in savings of the order of tens of thousands of dollars per year by eliminating the need to use elastic bands. Due to the fact that a band of string, once tied around a bunch of vegetables, has no ability to shrink further if it happens that the vegetables were not tightly bunched when the string was tied, it is important that the string be tied around the bunch as close as possible to the region at which the objects to be tied are clamped. The need to tie the bunches at a location as close as possible to the point at which the bunches are clamped is further dictated by the rather critical tolerances involved in tying a bunch of non-uniform objects that is moving along a conveyor line.
However, prior art bunching machines have generally been structurally unsuitable for use with an automatic tying machine. This unsuitability arises both from the structure of the prior art bunching machines and from the nature of the tying operation itself. The nature of known automatic tying machines is that they extend below the objects being tied and beyond the plane in which the string loop is formed. Prior art bunching machines such as the above referenced type have the clamping mechanism attached to each pocket. The provision of clamping members so disposed makes it impossible to located an automatic tying machine sufficiently close to the region of clamping to make the use of an automatic tying machine feasible. Also, prior art bunching machines having opposed clamping elements do not allow precise indexing of the tying mechanism with respect to the bunch. In order to tie a tight bunch, the string-carrying needle must come down as close to the rear of the bunch as possible. Due to non-uniformities in the bunch diameter, such prior art bunching machines only define the bunch center line and not the rear edge with precision.
Additionally, a number of difficulties have been encountered in adapting automatic tying machines for use with bunchers. These difficulties arise in part due to the need to reliably tie non-uniformly sized bunches of irregular shape. The situation is aggravated where, as in the present case, the bunches are moving. In such a situation, the placer foot mounted on the needle occasionally hits the product to be bunched, thus deflecting the needle and causing the apparatus to mistie or jam, with possible damage to the machine.
A further difficulty with prior art tying machines is that the string retaining mechanism is subject to unreliable operation due to the need to hold the two ends of the string loop securely during tying. The string retaining mechanism typically includes a clamping element that holds both ends of the loop. However, the normal tying process produces a short cut piece of string which tends to cause unreliable operation. In particular, if one of these pieces overlaps one of the string ends being held, the other end is not held securely. A similar problem arises when it is desired to use flat string. Certain shapes of objects to be tied, such as the generally tapered configuration of broccoli bunches, require the use of flat strings. Such string is prone to becoming folded along a longitudinally extending axis, so that when the single clamp is required to hold two flat strings, one of which is folded and so twice as thick, the other string end is improperly held. The presence of cut pieces of string compound this latter problem.
As mentioned above, it is important to tie a tight bunch. This requires the maintenance of proper string tension during the tying operation. In particular once the string loop is formed around the object to be tied, and the ends retained by the finger, the knotter bills take up a fixed amount of string as they turn. While it is possible to achieve reproducible results with regularly shaped objects of uniform compressibility, irregularly shaped and sized objects present a problem. If the retaining finger holds the string ends securely, the string can break or be tied too tightly, thereby injuring the possibly delicate product. If the string is not held securely, the result might simply be to pull the string out of the finger mechanism.
Therefore, while the use of an automatic tying machine in connection with automatic bunching machine is, in principle, highly advantageous, such use has not occurred, and the maximum economic benefit available from automatic bunching machines and automatic tying machines has not been realized.